The Underside

Siding under siding

A couple posts ago I removed the plaster and lath from one wall on the first floor in order to expose the sheathing from the inside. That in turn led to the question, what’s on the other side? If the sheathing is in good enough shape to keep and spray foam, we’ll also want to put rigid foam on the exterior to reach the desired R-value for our wall assembly.

Closed cell foam is about R-6.0 per inch, give or take. We have a wall cavity that is 3 3/4″ thick. Doing the math, 6 x 3.75 = R-22.5, which isn’t bad, but it’s not as high as we’d like. Even granting that we’d get an extra couple for sheathing and drywall, we’ll want two inches of rigid insulation on the outside. Using either rock wool or XPS would give us an additional R-10, bringing our total to around R-34, which is excellent. The advantage to rock wool on the exterior is that bugs don’t burrow through it as they can with XPS, plus it allows easier drying to the outside, preventing moisture from building up against the sheathing. Of course, it costs more.

So here’s the problem: under our vinyl siding is old siding. We knew this, but it turns out we didn’t know what we had. Inside the back porch is old wood siding, and we assumed the worst we’d have to deal with in removing old siding was lead paint. Unfortunately, it looks like the house was re-sided sometime after the porch was enclosed and before the vinyl siding was put on. That siding is made of cement, which almost certainly contains asbestos. You can see this siding in the photo above, where there’s a gap in the vinyl siding. We can also see it under the bottom edge of the siding along the sides of the house, and probably the front as well.

What’s under that remains a mystery. It could be the original sheathing, or new sheathing, or the old wood siding, or some combination thereof, since they didn’t necessarily do everything the same way. In any case, what to do with asbestos-laden siding? The good news is that this isn’t pressing. We’re not planning to do the exterior right away.

Our options are three-fold. The first is to leave it in place, put the insulation over it, and the siding over that. Encapsulation is a common way to deal with asbestos. I don’t like this option because our house is already so close to the neighbors (see the above photo) and I don’t think the end result will be even and look right. However, these aren’t very strong arguments. The second option is to pay an asbestos abatement company to remove the siding, probably at great expense. One rough estimate using a price per square foot I found online was $11,000. The final option is to remove it ourselves, following proper procedures to prevent any dust from spreading and disposing of it properly. That may be a good way to go, but it will depend on how much asbestos is in the siding. To figure that out, before we do anything we’ll have the siding tested. How much or how little asbestos it contains will determine our course of action.

I came up with a fourth option, but Sarah wasn’t thrilled with it: sell the house and buy one that doesn’t have asbestos siding!